1. Field of the Invention
This invention relates to the measurement and reduction of carbon in fly ash by employing microwave energy.
2. Description of the Prior Art
Microwave energy has been used in various ways in the coal processing environment. For example, U.S. Pat. No. 4,259,560 to Rhodes discloses a process for drying coal and other conductive materials using microwaves. The process involves drying coal particles as they fall freely in a chamber past a microwave source.
U.S. Pat. No. 4,282,066 to Wagener, et al. discloses a process and apparatus for coking coal using microwave radiation. After the coke is created, Wagener teaches the use of photocells to cool the coke by absorbing radiation therefrom.
U.S. Pat. No. 4,435,374 to Helm, Jr., discloses a method of producing carbon monoxide and hydrogen by gasification of solid carbonaceous material. This method involves the use of microwave irradiation to convert all types of coal to carbon monoxide and hydrogen. This process involves treating the solid carbonaceous material with steam.
None of the aforementioned methods are used to reduce and measure carbon in fly ash. Known methods for measuring and reducing carbon content in fly ash do not involve microwave radiation. Furthermore, present methods of collecting a sample of ash are cumbersome and manpower intensive. Normally, a sample is collected in a combustion byproducts duct that connects a combustion zone to a particulate collection and combustion gas purification zone. The sample is a very small fraction of the total amount of material in the duct at any point in time. Because the sample is only a small fraction of the amount actually produced in the combustion zone, a small inaccuracy in the sample results in a large miscalculation of actual conditions.
There remains a need for a method and apparatus for reducing the carbon content in fly ash and for an apparatus and method of measuring the amount of carbon in fly ash. This need also remains because much of the fly ash produced by the utility industry today contains unburned carbon. This unburned carbon represents a significant loss in energy efficiency and contributes to higher electricity generation costs. Fuel must be purchased to offset the carbon in the ash. Specifically, excess air is provided to consume the carbon in the fuel. The air that is provided to combust the unburned carbon is heated by additional fuel. As this additional air removes heat energy from the combustion process and is wasted, the combustion process has a lower efficiency than could be achieved had all of the carbon in the fuel been consumed.
There are also disposal cost increases because the unburned carbon represents greater bulk. Further, carbon in ash is detrimental to utilization of ash as a cement displacement material. Thus, a significant cost reduction would be realized if carbon in ash could be reduced more efficiently.
There remains, therefore, a real and substantial need for improved means for measurement and reduction of carbon in fly ash.